Impact tool

Abstract

An improved impact tool which has a cylinder, a liner mounted therein, a piston mounted in the liner and reciprocated by gas and hydraulic pressure, and a tubular valve slidably mounted on the liner for controlling a hydraulic circuit. The tubular valve is hydraulically pushed up and down without a spring being used. No gas accumulator is used. Thus, the impact tool has a simple construction and is durable.

What is claimed is: 
     
       1. An impact tool comprising: a cylinder;   a liner mounted therein with an annular space between said liner and said cylinder;   a piston reciprocably mounted in said liner and having an enlarged portion substantially midway of its length sealingly slidable in said liner and defining spaces in said liner above and below said piston;   a tool holder secured to the bottom of said cylinder for holding therein a tool to be hit by said piston upon the downward stroke of said piston;   said liner having a plurality of oil apertures therein between the interior of said liner and said annular space and spaced along the length of said liner for flow of hydraulic oil between said annular space and the spaces in said liner above and below said enlarged portion of said piston, and said cylinder having an outlet opening out of said annular space;   a tubular valve slidably mounted on said liner in said annular space for controlling the flow of hydraulic oil through said oil apertures into the space below said enlarged portion for pushing the piston up when said valve is in a lower position and for allowing the oil in said lastmentioned space to be discharged from the lastmentioned space when said valve is in an upper position and having a portion with an effective cross-sectional area exposed to hydraulic oil under pressure through one of said oil apertures when said piston is in the raised position for raising said tubular valve, said portion no longer being exposed to the hydraulic oil under pressure when said enlarged portion of said piston passes said one oil aperture on its downstroke;   at least one rod slidably mounted on the cylinder for movement substantially parallel to said piston and extending into said annular space and having one end engaging said tubular valve;   a gas reservoir provided above the cylinder for containing gas for being compressed as said piston moves up; and   a hydraulic circuit in said cylinder and said liner for supplying hydraulic oil said liner for flow through said oil apertures and to the other end of said rod against an effective cross-sectional area of said rod which is less than said effective cross-sectional area of said portion of tubular valve member for biasing said rod and said tubular valve down under hydraulic pressure when the tubular valve is in the upper position.   
     
     
       2. An impact tool as claimed in claim 1 in which said cylinder has a second liner mounted on said firstmentioned liner around the top thereof and having at least one hold therein parallel to the axis thereof which said rod is slidably mounted.